There is an electron microscope using electron beam as a microscope which allows magnified observation of a sample and it is utilized in observation of the detailed shape of the surface of the sample and the composition thereof. A scanning electron microscope (hereinafter, referred to as SEM) focuses an electron beam which has been accelerated by a voltage applied to an electron source by an electron lens, and scans the focused electron beam (a primary electron) on a sample by a reflector. An electron (a secondary electron) which has been emitted from the sample by being irradiated with the primary electron is detected by a detector. A secondary electron signal is detected in synchronization with a scanning signal to configure a two-dimensional image. Since the secondary electron yield emitted from the sample is made different in accordance with the shape of the sample surface, a difference is generated between detection signals and a contrast reflecting the shape can be obtained. In the SEM, observation of a fine surface shape is the most common application.
Recently, cases that a sample which is configured by an insulator or an insulator and a conductor becomes an observing object of the SEM have been increased. In a case where the object is the insulator, an image disturbance such as an image drift, a loss of shape contrast or the like during observation becomes a problem. This disturbance occurs because a voltage contrast which is generated by influence of electrical charging by electron beam irradiation on a detection amount of the secondary electrons is superimposed on the shape contrast. For the purpose of reducing the influence of the voltage contrast caused by the aforementioned electrical charging, a technique of performing imaging by controlling the number of electrons to be irradiated by pulsed the electron beams is disclosed in Non-Patent Literature 1. In Patent Literature 1, as a general technique of intermittently irradiating and pulsing an electron beam, a system of using a blanking electrode and a blanking slit is disclosed. In Patent Literature 2, an image capturing method of detecting a secondary electron by pulsed electron irradiation and configuring a two-dimensional image by a secondary electron signal from each irradiation position is disclosed. In Patent Literature 3, a method of irradiating the same place with a pulsed electron a plurality of times at predetermined time intervals to image it is disclosed.